In the semiconductor devices which are manufactured by the above described MEMS and have diaphragm structures and beam structures that are partially thinned, MEMS pressure sensors and MEMS acceleration sensors are included. Such sensors are generally manufactured by dividing a plurality of the above described diaphragm structures and beam structures individually after the diaphragm structures and beam structures are simultaneously formed in the semiconductor wafer process. For the division, the method for performing crushing by rotating a ring-shaped dicing saw in which particles of diamond and CBN are held by a bond material at a high speed is most commonly used. Since the machining by the dicing saw is performed while cutting water is run for washing out crushed chips and cooling down the frictional heat, and the diaphragm structures and the beam structures are brittle structures, there has been the problem that the diaphragm structures and the beam structures are broken due to the pressure of the cutting water during machining by the dicing saw.
In recent years, as a method for solving such a problem, machining by laser light has attracted attention, and an example of such machining is disclosed in, for example, Japanese Patent No. 3408805.
In the manufacturing method by laser light disclosed in Japanese Patent No. 3408805, a modified region by multiphoton absorption is formed in a semiconductor wafer, and the semiconductor wafer is divided by cleavage with the modified region as the starting point. Multiphoton absorption is the phenomenon in which even when energy of photon is smaller than the band gap of absorption of the material, namely, even when photon is optically transmitted, by making the intensity of light very high, absorption occurs in the material. By aligning the focusing point of laser light with the inside of the semiconductor wafer, the phenomenon of multiphoton absorption is caused, and the modified region is formed inside the semiconductor wafer. Then, by easily breaking the substrate along the dicing lane, with the modified region formed as the starting point, division without requiring cutting water is enabled.
The above described method for machining by laser light will be described based on the drawings. FIG. 9 is a plane view showing the division lines and the periphery of the semiconductor substrate which is a lased machining workpiece, and FIG. 10 is a sectional view taken along the line C-C′ shown in FIG. 9 during laser processing. In FIGS. 9 and 10, reference numeral 101 denotes a semiconductor substrate, reference numeral 102 denotes a semiconductor element which constitutes the semiconductor device formed in the semiconductor substrate 101, reference numeral 104 denotes the division line of the semiconductor element 102, reference numeral 108 denotes laser light, reference numeral 109 denotes a modified region, and reference numeral 110 denotes a cut portion (crack) occurring with the modified region 109 as the starting point.
The process of the method of machining by laser light will be described hereinafter.
First, the focusing point of the laser light 108 is aligned with the inside of the semiconductor substrate 101, and multiphoton absorption is caused in a predetermined thickness direction.
Next, by scanning the laser light 108 along the center of the division line 104 while causing multiphoton absorption continuously or intermittently, the modified region 109 along the division line 104 is formed inside the semiconductor substrate 101, and the cut portion 110 is formed.
Next, an external force is simultaneously applied to both ends of the semiconductor substrate 101, the semiconductor substrate 101 is split with the modified region 109 as the starting point, and the semiconductor device is formed. Since at this time, the cut portion 110 is formed with the modified region 109 as the starting point, the semiconductor substrate 101 can be easily broken with a relatively small external force. Especially when the semiconductor substrate 101 is thin, the semiconductor substrate 101 splits naturally in the thickness direction even if the external force is not especially applied to the semiconductor substrate 101.
Other than the above described method for machining by laser light, as the method for solving the problem in which diaphragm structures and beam structures are broken by the pressure of cutting water, reducing the thickness of the machined portion by forming in advance a groove on the division line by anisotropic etching or the like is performed. This method is disclosed in, for example, Japanese Patent Laid-Open No. 2001-127008.
In the manufacturing method disclosed in Japanese Patent Laid-Open No. 2001-127008, an etching protection film is formed on the semiconductor substrate of an orientation plane (100) so as to open the division line in the longitudinal direction and the lateral direction first, and thereafter, anisotropic etching is performed. Herein, etching is stopped on an orientation plane (111), and therefore, a V-groove with the angle of inclination of 54.7 degrees is formed. Next, an external force is applied to the semiconductor substrate so that the V-groove is enlarged to divide the semiconductor substrate along the V-groove, and the individual semiconductor devices are formed.
However, in the above-described known laser machining method disclosed in Patent Document 1, the following problem arises.
When the semiconductor substrate is thick, the semiconductor substrate cannot be divided with the modified region by one scanning. Therefore, a plurality of modified regions are required to be formed parallel to the thickness direction by carrying out laser machining a plurality of times, and this leads to increase in tact required for machining.
In the above-described known method of manufacturing in which the V-groove is formed, disclosed in Patent Document 2, the following problem arises.
Since in the portion where the V-grooves intersect with each other in the longitudinal direction and the lateral direction of the division lines, erosion of anisotropic etching differs from that in the other portions, etching does not stop in the orientation plane (111) if etching is performed excessively, and etching advances into an orientation plane (211), for example. In other words, when the V-groove is to be formed simultaneously with the step of forming the diaphragm structure requiring etching which is deeper than, for example, the V-groove, the intersection portions of the V-grooves are excessively etched, and the semiconductor substrate is penetrated. Therefore, the strength of the semiconductor substrate is extremely reduced, and the semiconductor substrate is broken at the time of handling the semiconductor substrate.